In off-the-road vehicles it is common to utilize a an implement such as a bucket for handling dirt wherein the bucket is utilized to lift the dirt as well as, in some vehicles, in a manner of a backhoe. In such a hydraulic system, it is desirable to be able to shake the bucket in order to dislodge mud, clay or debris from the bucket. It is also desirable to be able to penetrate frozen ground. Open center hydraulic systems commonly in use today are capable of rapidly shaking the bucket. On the other hand, where the hydraulic system comprises a directional valve for controlling flow to the hydraulic actuator of the bucket and a load sensing variable displacement pump for delivering fluid to the directional valve, the hydraulic system is not capable of providing rapid shaking of the bucket. Load sensing systems function more slowly to demand than comparable open center hydraulic systems. It is therefore desirable to provide a hydraulic circuit for load sensing variable displacement pump systems.
Accordingly, among the objectives of the present invention are to provide a hydraulic system for operating a bucket which includes a load sensing variable displacement pump wherein hydraulic fluid may be selectively provided to a directional valve so that it is readily available for shaking a bucket or the like; which can be readily adapted to present hydraulic systems; which can be adapted at relatively low cost in the modification of such systems; which overlaps any delay as presently occurs in load sensing variable displacement pump systems.
In accordance with the invention, in a hydraulic system for a vehicle that includes an implement such as a bucket that is operated by a hydraulic actuator, a directional valve which controls flow from a load sensing variable displacement pump, a hydraulic bucket shake circuit is provided which is selectively operable to force the pump to a maximum displacement condition thereby providing standby pressure and flow to the directional valve so that the directional valve can be operated rapidly in order to shake the bucket and dislodge mud, clay and debris from the bucket or to allow penetration into frozen ground.